Add shipit.pathmap to get triggering

Summary:
X-link: facebookincubator/zstrong#866

Build triggering works by using entries in shipit.pathmap, however for
Glean we're using the native ShipIt so we didn't have these. Add a
dummy shipit.pathmap section to enable triggering.

Reviewed By: josefs

Differential Revision: D58146311

fbshipit-source-id: 45ce5a707584d834a4de452029cc0699abb0df82

build/fbcode_builder/manifests/glean

@@ -4,6 +4,12 @@ fbsource_path = fbcode/glean
 shipit_project = facebookincubator/Glean
 use_shipit = true
 
+[shipit.pathmap]
+# These are only used by target determinator to trigger builds, the
+# real path mappings are in the ShipIt config.
+fbcode/glean = glean
+fbcode/common/hs = hsthrift
+
 [subprojects]
 hsthrift = hsthrift